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up counter need help

Discussion in 'Electronics Homework Help' started by vead, Jan 28, 2014.

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  1. vead

    vead

    473
    14
    Nov 27, 2011
    table for 3 bit up counter

    present state next state
    N A B C
    0 0 0 0 0 0 1
    1 0 0 1 0 1 0
    2 0 1 0 0 1 1
    3 0 1 1 1 0 0
    4 1 0 0 1 0 1
    5 1 0 1 1 1 0
    6 1 1 0 1 1 1
    7 1 1 1 0 0 0

    present state I think present state means this
    N A B C
    0 0 0 0
    1 0 0 1
    2 0 1 0
    3 0 1 1
    4 1 0 0
    5 1 0 1
    6 1 1 0

    next state means

    N A B C
    1 0 0 1
    2 0 1 0
    3 0 1 1
    4 1 0 0
    5 1 0 1
    6 1 1 0
    7 1 1 1
    0 0 0 0


    that's circuit is very complex for me don't know any idea what i do next
    1)how to find out input for counter
    2)how to find out output for counter
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,562
    2,354
    Nov 17, 2011
    a) N= number of the state in decimal, not required for the logic.

    b) Input and output are given:
    output = present state
    input = next state
    Plus a clock to make it count.

    The counter has three flipflops: A, B and C with associated states 000, 001, 010 etc.
    Input tho the counter is the current state and a clock. The logic needs to find the nect state from the current state. The clock will then enter the new state into the flipflops with the active clock edge.

    Example:
    Current state: A=00, B=0, C=0 (000). next state: A=0, B=0, C=1 (001)
    Find the logic that creates output 001 from input 000. The output of this logic is input to the D-input of the flipflops. The flipflops will change from 000 to 001 with the next clock.
    Repeat for the other states. minimize the resulting logic to use few gates.

    Tip: use a Karnaughh diagram to minimize the logic.
     
  3. vead

    vead

    473
    14
    Nov 27, 2011
    I try k map for D0 flip flop
    A B C D0
    0 0 1 0
    0 1 0 0
    0 1 1 0
    1 0 0 0
    1 0 1 1
    1 1 0 1
    1 1 1 1
    0 0 0 1

    K map

    A/BC 00 01 11 10

    1 0 0 0
    1 1 1 1

    I am not sure that I am correct

    how to find out output D0 (equations)
     
  4. mursal

    mursal

    75
    0
    Dec 13, 2013
    You need to use a flip-flop to divide the clock input by 2. 3 flip flips will give you a binary count 0 to 7 (000 - 111). Click

    Hope this helps, good luck
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    10,562
    2,354
    Nov 17, 2011
    Mursal linked you to an asnchronous counter. That is one possible solution.
    I tipped you to a synchronous counter. That is another solution.

    Both realizations have advantages and disadvantages. From what you gave us in your original post, both realizations will lead to a valid result.


    For the synchronous counter:
    Your attempt at a K-map I do not understand. You have three inputs A,B and C You will need three outputs A', B' and C' which represent the next state and will be latched into the flipflops with the next clock. A single output D0 of the logic will lead to no result.

    Read this tutorial on the design of synchronous counters.

    By the way, I'm quite sure this is homework, so I will move this thread in the relevant section.
     
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